As used herein, tissue culture refers to the process by which tissue cells are grown in vitro, i.e., in artificial media under relatively controlled conditions.
In general, tissue cells are grown either in suspension or attached to a solid support. Some cells do not need a solid support and can also grow in a suspended condition. However, other cells grow only when attached to a surface, i.e., anchorage-dependent cells. The term anchorable cells is used herein to include both types of cells.
At the present time, perhaps the most common large scale tissue culture procedure involves the use of multiple roller bottles. As noted by Jensen, Biotechnol. Bioeng., 23, 2703 (1981), roller bottle culturing is extremely expensive, requiring intensive labor and considerable capital outlay for incubation equipment. Another disadvantage is an increased risk of contamination because the roller bottle procedure is essentially a batch process involving hundreds of separate manipulations.
Many recent innovations have been directed to overcoming these drawbacks. Examples of such innovations include, by way of illustration only, microcarrier beads, artificial capillaries (hollow fibers), and bundled tubes. Indeed, some efforts have been directed to improving roller bottles themselves.
U.S. Pat. No. 4,317,886 discloses a roller bottle comprising an outer housing defining a hollow chamber therein, with at least one annular member placed inside the chamber spaced a short radial distance inwardly from the outer housing. In effect, the disclosed roller bottle is equivalent to a series of increasingly smaller roller bottles located within a single housing.
Another way to increase the surface area in a conventional roller bottle is disclosed in U.S. Pat. No. 3,853,712. Here, a flexible strip is wound or otherwise formed by successive changes of direction into a compact cell support which can fit inside a roller bottle. As an example, a length of corrugated strip material and a length of smooth, planar strip material were wound together into a self-spacing spiral.
While the use of microcarriers for culturing mammalian anchorage-dependent cells in suspension has been given increasing attention in recent years, such use is not directly related to the present invention. Microcarrier culture systems are based on suspending literally millions of individual, minute beads, not monolithic supports.
Of more immediate interest is the use of a plurality of tubes for growing anchorable cells. By way of illustration, U.S. Pat. No. 3,732,149 discloses an apparatus which comprises a plurality of mutually parallel columns having a uniform length. These columns are clamped together at the ends by manifolds which are fixed onto a shaft which is parallel to the columns. In use, the cells grow on the inner surfaces of the columns, through which media is pumped. The entire device is rotated about the shaft. In effect, the disclosed apparatus is a variation of the roller bottle technique.
A somewhat similar device also is disclosed in U.S. Pat. No. 3,827,943. Here individual tubes having an internal diameter of from 1 to 10 cm have a single inlet/outlet tube. This feature allegedly reduces the risk of infection.
Another variation of the bundled tube concept is the Gyrogen. While similar in configuration to the two devices discussed above, it differs in that media is circulated both through and around the tubes. Thus, cells are able to attach on both the internal and external surfaces of the tubes. As with the preceding bundled tube devices, the entire apparatus is rotated about a central axis. See, e.g., H. C. Girard et al., Biotechnol. Bioeng., 22, 477 (1980).
It should be noted that the bundled tube process and variations thereof, should not be confused with the artificial capillary or hollow fiber concept. They are distinct. In the artificial capillary process, the cells and medium do not mix. For example, the cells attach to the outer surfaces of the capillaries, while the nutrient medium flows through the capillaries. Nutrient substances diffuse through the capillary walls and into the cells, while cell products or metabolites diffuse from the cells through the capillary wall into the medium. See U.S. Pat. No. 3,883,393; J. K. Kan et al., Biotechnol. Bioeng., 20, 217 (1978); and U.S. Pat. No. 4,075,092.
Another means of increasing the surface area to volume ratio of a culture vessel is to pack the culture vessel with bits of inert material. One disclosure states that a double-walled cylindrical glass vessel can be filled with segments of glass tubing of about 6 mm in length to increase the surface area. The reaction vessel was part of an instrument or apparatus having automatic gas and medium control. See, E. Harms et al., Cytobiologie, 18, 67 (1978).
For recent summaries of tissue culture in general, see T. Cartwright et al., Process Biochemistry, 13, 3 (1978); L. Keay et al., Process Biochemistry, 14, 17 (1979); and M. D. Jensen, supra.
Finally, an embodiment of the supports useful in the preparation of the present immobilized animal or plant cell composite has been described as a support for enzymes and microbes. Specifically, M. R. Benoit et al., Biotechnol. Bioeng., 27 1617 (1975), describes the immobilization of catalase on commercially available monolithic catalyst supports. The enzyme was covalently coupled to the support by means of an intermediate silane coupling agent activated with glutaraldehyde.
As a microbial support, a monolithic substrate was used in a study of acetic acid production by immobilized Acetobacter aceti cells. These cells were allowed to attach to a ceramic support, cordierite, by adsorption. See C. Ghommidh et al., Biotechnol. Bioeng., 24, 605 (1982), a reference appears to be based, at least in part, upon a thesis by C. Ghommidh, which was published in 1980.